Switch networks are employed to route data from output ports to input ports of various kinds of nodes, including processors, memory, circuit boards, servers, storage servers, external network connections or any other data processing, storing, or transmitting device. In large scale computer systems, scalable packet switch networks are used to connect ports. In order to build switch networks that can scale to a large number of ports, it is desirable for the basic switch component to have as many inputs and outputs as possible. This means that a switch network that can span all the ports and can be constructed with fewer stages. In switch networks with N log (N) growth characteristics, such as Clos networks, this is termed a high radix router, since a large switch component size reduces the logarithmic growth term in network complexity. Where electronic devices are used for switching, the overall external bandwidth of each switch component is constrained so that the system designer is forced to compromise between the number of channels on and off the switch, and the bandwidth of the channels. For example, the same silicon technology can implement a 64×64 switch with each channel operating at 40 Gbit/s or a 16×16 switch with each channel operating at 160 Gbit/s. This constraint arises for the maximum number of signal connections for a package and the data rate for the signals themselves. The signal data rate is determined by the power and signal integrity considerations.
Switch networks can often be a data processing bottleneck for computing environments. A typical switch network, for example, can limit the scope of a computing environment's ability to handle the ever increasing data processing and transmission needs of many applications, because many switch networks are fabricated to accommodate only the “port-rate of the day” and the “port-count of the day” and are not fabricated to accommodate larger bandwidths that may be needed to effectively accommodate future applications. In particular, the amount and frequency with which data is exchanged between certain ports can be larger for some ports than for others, and the use of low-latency, metal-signal lines employed by most switch networks have limited bandwidths. As a result, the amount of data that can be transmitted between ports may not be well matched to the data transfer needs of the ports employed by an application at each point in time, which often results in data processing and/or transmission delays. Switch networks have a large number of long signal line intra-chip connections arising from the need to connect any input to any output. These long signal lines consume significant amounts of power in the repeaters needed to overcome electronic transmission losses.
A number of the issues associated with electronic signals transmitted via signal lines can be significantly reduced by encoding the same information in particular wavelengths or channels of light transmitted via waveguides. First, the data transmission rate can be increased significantly due to the much larger bandwidth provided by waveguides. Second, degradation or loss per unit length is much less for light transmitted via waveguides than for electronic signals transmitted via signal lines. Thus, power consumption per transmitted bit is lower for light transmitted via waveguides than for transmitting the same data in electronic signals via signal lines.
Optical switch components have been constructed using a variety of different technologies such as micro-electro-mechanical systems, and magneto optic effects. However, these switches are all circuit switches, where configuring the switch is performed by a separate, generally electronic, control plane. A packet switch is distinguished from a circuit switch by the ability to make connections according to routing information embedded in the input data stream. A packet switch typically permits buffering of input data when the requested output is in use. Many electronic packet switches have been constructed. However, these network switches are limited in their ability to scale to meet demands of future higher performance processors. There are two limiting factors. First, the bandwidth on and off the router chips is limited, both in terms of the number of input/outputs (“IOs”), limited by packaging technology, and IO speed which is limited by signal integrity considerations. Second, the power required for the inter- and intra-chip communications grows significantly with higher IO counts and higher data rates.
Engineers have recognized a need for fast network switches that can accommodate data encoded light as a medium for transmitting massive amounts of data between various kinds of data processing, storing, or transmitting devices.